style.css

* {
    padding: 0;
    margin: 0;
    box-sizing: border-box;
}

.main-div {
    width: 100vw;
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    flex-direction: column;
    background-image: url("https://i.pinimg.com/originals/bf/7f/e6/bf7fe677458b68ee2228e8547c532b9c.jpg");
    background-position: center;
    background-size: cover;
    background-repeat: no-repeat;
    font-family: sans-serif;
    padding: 20px;
}

h1 {
    font-size: 40px;
    margin-bottom: 10px;
    text-shadow: 1px 1px 10px rgba(255, 255, 255, 80%);
    color: #502775;
}

.User-Name-Input,
.Quantity-Increase-Input {
    background-color: rgba(255, 255, 255, 40%);
    color: #502775;
    border: 1.5px solid #502775;
    border-radius: 5px;
    width: 80%;
    margin: 10px auto;
    padding: 15px 20px;
    font-size: medium;
    font-weight: 550;
    outline: none;
}

.Submit-Btn {
    font-size: 22px;
    border-radius: 5px;
    width: 100%;
    max-width: 400px;
    border: none;
    background-color: #502775;
    color: white;
    margin: 25px 15px;
    padding: 5px 20px;
    box-shadow: 1px 1px 10px rgba(255, 255, 255, 80%);
    letter-spacing: 1.5px;
    cursor: pointer;
    font-weight: bold;
    transition: all .5s;
}

.Submit-Btn:hover {
    background-color: #814fad;
}